Off-white potash feldspar and plagioclase are often difficult to distinguish on hand specimens. At this time, we must carefully observe the double crystal characteristics of these two feldspars, because plagioclase has double crystals, and when rotating the hand specimen, we can see that there are regular light and dark aggregates on the plagioclase crystals, and potash feldspar It is a cassette double crystal, which appears as two halves of crystals with different degrees of brightness.
Granite can be further named according to the types of dark minerals. For example, the dark minerals are mainly biotite, which can be called biotite granite, which is a common type of granite. If the content of biotite and muscovite are nearly equal, it can be called two-mica granite. If the dark mineral is mainly hornblende, it is called hornblende granite. If the dark mineral is mainly pyroxene, it is called pyroxene. Stone granite, which contains almost no dark minerals, can be called white granite.
